Reamers
Hole-finishing geometry, stock allowance, flute and coolant arrangements, and the distinction between tool size and finished-hole acceptance.
Tags: tooling, reaming, holemaking, finishing
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Reaming an ideal 9.80 mm pre-hole to 10.00 mm over 40.0 mm removes 124.41 mm³. The stock is 0.20 mm diametral, or 0.10 mm radial. Interpreting 0.20 mm as radial instead would remove 246.30 mm³. Check the actual pre-hole, runout, lead and bottom clearance.
Function and hole preparation
A reamer finishes an existing hole. Sandvik ties results to allowance, runout, alignment, clamping and coolant. Too little stock can cause rubbing. Sandvik Coromant, What is reaming?
Conventional reaming generally follows the prepared hole. Gühring's preparation guidance warns that this does not eliminate misalignment errors, while its separate face-reamer description identifies a specialized cutting-face design that need not follow the hole in the same way. The distinction limits a useful general rule: a conventional reamer is not a reliable substitute for correcting a misplaced hole, and specialized face-cutting capabilities cannot be inferred from the generic tool name. Gühring, Reaming tools, preparation and face-reamer sections.
Lead, guide and tool family
The lead is the tapered cutting entrance; the guiding portion supports the tool in the bore. Gühring describes hand reamers with a longer chamfer lead and a driving square, and machine reamers with shorter leads and machine holding arrangements. It also distinguishes adjustable, tapered and high-performance designs. A taper reamer makes a tapered opening rather than a nominally constant cylindrical bore. These are different geometries and interfaces, not synonyms for an interchangeable finishing tool. Gühring, reamer types.
Sandvik's general account places cutting at the bevel and taper leads rather than the lands. Its maintenance discussion consequently distinguishes sharpening the leads from changing the rest of the tool. The cutting entrance, guiding diameter and overall length have different functions; a long tool does not establish equally long usable cylindrical cutting depth in a blind hole. Sandvik, reamer geometry and maintenance.
Flutes, chip direction and coolant
Hannibal's Reamer Guide gives these application descriptions for its tooling:
| Flute arrangement | Described application relationship |
|---|---|
| Straight | Favored for short/non-chip-forming materials such as cast iron, bronze and free-cutting brass; through holes preferred |
| Right-hand spiral | Draws chips back out of a blind hole; the guide notes possible oversize cutting from the aggressive geometry |
| Left-hand spiral | Pushes chips ahead, favoring through-hole exit |
The same guide associates axial, center-fed coolant with blind holes and radial, flute-fed coolant with through holes. These are scoped application relationships; helix direction, cutting rotation and coolant-outlet geometry remain separate attributes. It also treats material-specific carbide grade and geometry as consequential. Hannibal Carbide, Reamer Guide, printed pp. 23–24.
A named product illustrates those boundaries. Gühring series 1037, HR 500 Guss D, is listed as carbide, right-hand cutting, Signum-coated, internally cooled and intended for through holes. Its H7 label describes the catalog offering; it does not prove that an arbitrary setup produces a conforming hole. Internal coolant alone does not make this series a blind-hole tool. Gühring series 1037.
Allowance and assembly behavior
A diametral allowance and a radial depth differ by a factor of two for an ideal coaxial cylindrical enlargement. Hannibal illustrates finish stock as a diametral difference, expressed as a percentage of tool diameter. This is scoped starting guidance; runout, holding, overhang and rigidity still affect the result. Hannibal, printed p. 24.
Explanatory synthesis: an oversized, tapered or interrupted prepared hole can present uneven stock around the circumference. A nominal drill marking does not establish the actual pre-hole diameter. Likewise, a reamer's diameter is not a measurement of the finished hole after alignment error, wear, deflection or material response. Sufficient coolant at the cutting region and adequate chip space concern the whole assembly, not merely the presence of an internal passage.
Worked example: diametral versus radial allowance
Use the example’s coaxial cylinders over 40.0 mm, excluding lead geometry, radii, runout, deformation and finish tolerances.
Diametral allowance = 10.00 − 9.80 = 0.20 mm
Radial depth = 0.20 / 2 = 0.10 mm
Removed area = π/4 × (10.00² − 9.80²) = 3.1102 mm²
Removed volume = 3.1102 × 40.0 = 124.41 mm³
If the same 0.20 mm were instead interpreted as radial stock, the pre-hole would be 9.60 mm. The removed volume would then be π/4 × (10.00² − 9.60²) × 40.0 = 246.30 mm³, approximately 1.98 times the first volume. The nonlinear area relationship makes this slightly less than exactly double.
For a blind hole, account for actual lead and bottom clearance beyond the cylindrical length. Check torque, chip form and tool life in the real setup.
Finished-hole and source limits
Diameter, roundness, straightness, position and surface texture are distinct results. A size measurement or a nominal fit label does not independently prove all of them. A smooth wall can coexist with a misplaced axis or a tapered bore. Tool and hole tolerances therefore describe different objects, and neither alone establishes a particular assembly fit.
The live Sandvik and Gühring pages reviewed on November 2, 2026 PST have no separately verified technical issue dates. The retrieved Hannibal extract carries printed pages 23–29 without a verified issue date; its upload directory is not an edition date. This article adopts no universal tolerance, reaming allowance, feed, speed or coolant recipe.